There exists a variety of different kinds of covers for swimming pools. Some covers consist simply of plastic sheets having grommets or tie-downs spaced around their perimeters for connection to fastening points at the edges of the swimming pool. Such covers do not really float on the surface of the water in the pool. They are used mainly to exclude leaves and other debris from the pool when the pool is not being used for a prolonged period. There also exist covers composed of a pair of plastic sheets which are laminated together to form small bubbles throughout the area of the cover. These bubbles contain trapped air and displace enough volume so that the cover can float on the surface of the water in the pool. In some cases, the covers may be given a dark color so that the covers are effective absorbers of sunlight for heating the underlying water in the swimming pool to some extent. However, considering the small surface-to-volume ratio of most swimming pools, that heating effect is minimal end is confined to a relatively thin layer of water just below the cover.
It is also been known to use conventional rigid solar panels to heat water in swimming pools. Such panels are usually positioned near the pool and are included in the water circulation loop serving the pool. However, such solar panel installations are usually quite expensive, visually intrusive and occupy a relatively large amount of space.